There is a constant endeavor to increase the speed by which integrated circuits can process digital information. By increasing the speed of integrated circuits, more information can be processed per unit time. The importance of high speed integrated circuit is evident, especially with digital integrated circuits, where successive generations of circuits have achieved faster switching speeds and lower propagation delays from the input to the output.
While new techniques are continually being developed to improve the speed characteristics of integrated circuits, little is being done to collectively preserve the high speed nature of a number of integrated circuits connected together on a circuit module to provide an overall function. Even though an integrated circuit may have internal high speed characteristics, such characteristics may not be fully realized when interconnected with other integrated circuits.
One approach for combining the functions of various integrated circuits is to provide a phenolic or fiberglass printed wire board, or printed circuit board, on which a number of integrated circuits may be mounted. Dual in-like or flat package integrated circuit chip carriers can be soldered or inserted into sockets in the printed wire boards. Such printed wire boards are constructed using metallic conductive paths for interconnecting the inputs and outputs of the various integrated circuits together to provide a desired function. The printed wire boards may even be connected to a printed wire backplane, so as to electrically combine other similar printed wire boards. This arrangement is typically utilized in building electrical apparatus, such as computers, minicomputers and a host of other electrical systems.
The packing density by which integrated circuits can be mounted to such printed wire boards is determined primarily by the size of the integrated circuit. As more circuitry is required, the printed wire boards become successively larger, and thus the distance between certain ones of the integrated circuits becomes greater. In high speed date processing equipment, the spacing between integrated circuits becomes critical, in that such spacing is proportional to the time by which signals can be transferred between the integrated circuits. As the interconnecting paths between integrated circuits becomes greater, the distributed capacitance associated with such path also increases, thereby adding to the time which it takes for a signal to propagate from one integrated circuit to another. Therefore, unless particular precautions are taken in packaging multiple integrated circuits, the individual high speed characteristics thereof may not be fully realized.
A microprocessor integrated circuit operating in conjunction with a number of integrated circuit memories is illustrative of the above-noted problem. Present microprocessor integrated circuits are capable of high speed exchanges of data between the memories to perform a task according to a software program. With the constant exchange of information between the microprocessor and the associated memories, it is imperative that the speed characteristics of the integrated circuits not be compromised by the manner in which the circuits are connected together. Optimum performance of the microprocessor requires that it be connected as closely as possible to the circuits most often accessed, namely the memories. In the ordinary course of operation, microprocessors can exchange millions of bits of data information per second with the associated memories. Any delay in exchanging data between the microprocessor and the memory is cumulative, and thus is a significant factor to consider in the design of a microprocessor controlled system.
From the foregoing, it can be seen that a need exists for an improved method and apparatus for packaging high speed integrated circuits, such as microprocessors and companion memories. A need also exists for packaging plural integrated circuit chips together, rather than the dual in-line of flat package carriers which typically contain the chips. An associated need exists for the construction of a high density package which is compatible with the manufacture of the integrated circuit chips themselves.